The present invention relates to a method of manufacturing a head suspension assembly used for a magnetic disk device, which includes a slider with at least one thin-film magnetic head element, a resilient suspension for supporting the slider and a head IC chip.
In such magnetic disk device, the thin-film magnetic head element for writing magnetic information into and/or reading magnetic information from a magnetic disk is in general formed on the slider flying in operation above the rotating magnetic disk. The slider is supported by the suspension made of a resilient thin metal plate extended from one end of each movable arm of the magnetic disk device.
Recently, recording frequency in the magnetic disk has rapidly increased to satisfy the requirement for ever increasing data storage capacities and densities in today""s magnetic disk devices. In order to realize higher frequency recording, proposed is a head suspension assembly structure with a suspension for supporting both a slider and a head IC chip of a driver circuit for the magnetic head element. According to this structure, since the length of lead lines from the driver circuit to the magnetic head element can be shortened, generation of unnecessary noises from the lead lines can be effectively suppressed, resulting in an improvement of high frequency recording characteristics.
In fabricating such a magnetic disk device, according a conventional method, each of the head IC chips was mounted on and connected to a connection conductor formed on a suspension by flip chip bonding with a reflow soldering process. Before performing the reflow soldering process, flux was applied to the connection conductor, and then the IC chip with bump balls of solder material was bonded by soldering. More concretely, processes called C4 (Controlled Collapse Chip Connection) including (a) flux applying process, (b) flip chip bonding process, (c) reflow soldering process, (d) cleaning process, (e) dry process, and (f) underfill injection and filling process were sequentially performed.
As will be noted, if the flip chip bonding is performed by reflow soldering using flux, it is necessary to execute the cleaning process after bonding. Namely, in reflow heat bonding, flux is applied to the suspension at a position to which the IC chip is bonded, in order to prompt melting of the solder and temporarily adhere the IC chip to the suspension during reflow soldering. However, since the applied flux may have the adverse effect of producing gas, for example, cleaning has to be done after bonding.
It is desired to fill an underfill into a clearance between the connection conductor on the suspension and the head IC chip to improve heat radiation characteristics, to improve mechanical strength of this area, and to cover a part of the IC chip. However, this filling of the underfill has to be done after the cleaning process. Therefore, according to the conventional fabrication method, after the IC chip had been bonded to the connection conductor on the suspension and then the cleaning process had been finished, the filling of the underfill into the clearance between the connection conductor and the head IC chip was executed by injection.
However, it is very difficult to fill the underfill by injection into the extremely narrow clearance which will be typically 50 xcexcm or less. Therefore, working time and inspection time become long, causing lead time, which is the processing time of the whole manufacturing process, to increase, and manufacturing cost also increases.
It is therefore an object of the present invention to provide a method of manufacturing a head suspension assembly, whereby working time and inspection time can be shortened and inspection can be simplified.
Another object of the present invention is to provide a method of manufacturing a head suspension assembly, whereby manufacturing cost can be reduced.
According to the present invention, a method of manufacturing a head suspension assembly includes attaching underfill to a portion on which an IC chip with a circuit for a thin-film magnetic head element is to be mounted, disposing the IC chip on the attached underfill, and performing ultrasonic bonding of the IC chip.
According to the present invention, furthermore, a method of manufacturing a head suspension assembly which has a magnetic head slider with at least one thin-film magnetic head element, a support member for supporting the magnetic head slider, an IC chip with a circuit for the at least one thin-film magnetic head element, a lead conductor member on which the IC chip is bonded, and underfill filled in a clearance between a bottom face of the IC chip and the lead conductor member, is provided. The method includes attaching underfill to a mounting position of the lead conductor member at which position the IC chip is mounted, and thereafter, performing ultrasonic bonding of the IC chip with the lead conductor member.
Since filling of the underfill can be done only by attaching it before bonding of the IC chip, the underfill filling process can be extremely simplified. As a result, working time and inspection time can be shortened and inspection process can be simplified. Thus, manufacturing cost can be reduced.
Due to ultrasonic bonding, it is not necessary to pass the IC chips that are weak from heat stress through a high temperature reflow furnace. Therefore, reliability of finished head suspension assemblies can be improved and also yield of head suspension assemblies can be improved. Furthermore, because no reflow soldering process that requires very long processing time is needed, the working time can be further decreased.
In addition, no reflow soldering results in no cleaning process. The magnetic head slider crosses the surface of the magnetic disk with a very minute crevice between the slider and the magnetic-disk surface. In order to secure the minute crevice, it is very important to maintain a bending angle of each suspension for supporting the slider even after the cleaning process. Since injection or ultrasonic vibration of washing liquid is executed during cleaning process, it is difficult to clean the assemblies without changing the bending angle of the suspensions. However, according to the present invention, since no cleaning process is done, the above-mentioned problems are certainly resolved.
Since there is no reflow soldering, there is no flux application process causing the number of fabricating processes to further reduce.
In reflow soldering it is difficult to correctly control the fused amount of solder and thus the IC chip will freely descend to abut the connection terminals by its own weight. Therefore, according to the conventional method, sufficient stability in bonded size of the assemblies cannot be expected. However, according to the present invention, since ultrasonic bonding is adopted instead of reflow soldering, the stability in bonded size of the assemblies can be greatly improved by controlling energy during the bonding.
As the suspension has a plate spring structure, the bonding face of the suspension inclines against the attachment part of the base plate. In the reflow soldering process, since it is necessary to support to keep the bonding face horizontal in order to obtain effective heat conduction and to melt uniformly the solder bumps of the IC chip, the inclination of the bonding face must be taken into consideration. However, according to the present invention, by adopting ultrasonic bonding, it is necessary that the bonding face of the suspension is horizontal. Therefore, easier bonding of the IC chip can be expected.
It is preferred that the lead conductor member has a first portion formed on the support member and a second portion elongated out of the support member, and that the mounting position is located within the first portion or the second portion of the lead conductor member.
It is also preferred that the method further includes forming of Au or Cu bumps on first connection terminals of the IC chip before the ultrasonic bonding. In this case, the forming of Au or Cu bumps may include forming of Au or Cu bumps on the first connection terminals by using Au or Cu balls.
It is preferred that the method further includes forming of Au or Cu pads as second connection terminals to which the first connection terminals of the IC chip are bonded, before the ultrasonic bonding.
It is also preferred that the method further includes forming of Au or Cu bumps on second connection terminals to which first connection terminals of the IC chip are bonded, before the ultrasonic bonding. In this case, the forming of Au or Cu bumps may include forming of Au or Cu bumps on the second connection terminals by using Au or Cu balls.
It is preferred that the method further includes forming of Au or Cu pads as the first connection terminals of the IC chip before the ultrasonic bonding.
As the size of the head IC chip is very small, bump ball size should be small and a pitch between the bumps should be large when solder balls are adopted and the reflow soldering is executed. However, by using Au or Cu balls according to the present invention, not only the bump size by also the bump pitch may be small. Thus, bumps can be formed very easily. The smaller bump pitch results in high density bumps and therefore the chip size can be more reduced.
In general, if solder contains large quantities of Au, mechanical strength of the bonding lowers. Thus, according to the conventional method adopting the solder balls, the Au layer of the connection terminals in the lead conductor member must be extremely thin. However, by adopting the Au balls instead of the solder balls, the thickness of the Au layer of the connection terminals can be optionally determined.
Furthermore, according to the conventional method adopting the solder balls, there is no means for controlling fused height of the solder bumps and thus the IC chip will descend and tend to incline by its own weight depending upon the bump layout of the IC chip. However, by adopting ultrasonic bonding of Au or Cu balls according to the present invention, it is possible to easily keep the bonding face of the IC chip horizontal and to control the distance between the bottom face of the IC chip and the lead conductor member at a desired value.
It is preferred that the underfill attaching includes dropping the underfill to the mounting position of the lead conductor member. In this case, preferably the dropping of the underfill is executed so that a central part of the attached underfill has a convex form toward the upper part. Since the underfill is dropped to obtain a convex form when the IC chip is placed on the underfill, the clearance between the bottom face of the IC chip and the surface of the lead conductor member is filled with the underfill without forming any cavity.
Further objects and advantages of the present invention will be apparent from the following description of the preferred embodiments of the invention as illustrated in the accompanying drawings.